The invention relates to an end station for wire telecommunication comprising terminals for connecting the end station to at least a two-wire line of a telecommunication network, the end station comprising a line coupling arrangement having a terminating impedance for providing a match of the end station impedance with a line impedance of the telecommunication network, and further a control arrangement for controlling the line coupling arrangement. Such end stations for speech and/or data communication may be telephone sets, apparatus for modem traffic among personal computers or telefax devices and may also be other apparatus for wire telecommunication.
An end station of this type is generally known as an electronic telephone set as described in Philips Data Handbook "ICs for Telecom Subscriber Sets, Cordless Telephones, Mobile/Cellular Radio Pagers CA3089 to PCD44 13", Data Handbooks IC03a and IC03b, 1991. On page 851 of said handbook a block diagram of such an end station is shown comprising terminals a/b, b/a for connecting the end station to a two-wire line of a telecommunication network, a telephone line. The end station comprises a line coupling arrangement in the form of a transmission circuit, for example, the IC type TEA1067, and a control arrangement in the form of a microcontroller designed for telephony purposes, for example, the IC type PCD3349. Furthermore, a representation is given of a kaypad coupled to the microcontroller and a microphone and telephone generally designed as a telephone receiver coupled to the transmission circuit. The microcontroller, a microprocessor comprising a ROM memory, RAM memory and special I/O units, produces, for example, control signals for the transmission circuit or line coupling arrangement. Page 1460 of said handbook shows a block diagram of the IC type TEA1067, a bipolar IC, and page 1476 shows the IC type TEA1067 comprising external components for connection to the public telephone network. In the application shown on page 1476 the dynamic impedance in the audio frequency range, or terminating impedance is largely determined by an external component R1, here a 620 .OMEGA. resistor, as described on page 1462.
Network managers in various countries pose different requirements as regards matching a telephone set with the telephone line. Although a 600 .OMEGA. telephone set impedance has so far been rather customary, there is now a tendency towards changing to a complex telephone set impedance satisfying the requirements of network managers. For example, the required telephone set impedance in general may be described as a unipolar complex impedance having different specified parameters for different network managers. A further tendency is to avoid using external components as much as possible when ICs are structured into an end station. Introducing large capacitances on the IC, as is generally the case with complex telephone set impedances, will cause problems. Furthermore, in an absolute sense it is impossible in practice to realize accurate impedances on an IC. When external impedances are used for obtaining a desired telephone set impedance, there is the disadvantage that the telephone set must comprise different external components for different countries, so that no flexibility is possible on the IC when the set impedance has been realized.